全文获取类型
收费全文 | 1077篇 |
免费 | 175篇 |
国内免费 | 149篇 |
专业分类
化学 | 831篇 |
晶体学 | 18篇 |
力学 | 68篇 |
数学 | 81篇 |
物理学 | 403篇 |
出版年
2023年 | 23篇 |
2022年 | 38篇 |
2021年 | 52篇 |
2020年 | 45篇 |
2019年 | 54篇 |
2018年 | 32篇 |
2017年 | 39篇 |
2016年 | 53篇 |
2015年 | 63篇 |
2014年 | 71篇 |
2013年 | 78篇 |
2012年 | 100篇 |
2011年 | 121篇 |
2010年 | 63篇 |
2009年 | 66篇 |
2008年 | 55篇 |
2007年 | 55篇 |
2006年 | 60篇 |
2005年 | 41篇 |
2004年 | 48篇 |
2003年 | 31篇 |
2002年 | 26篇 |
2001年 | 13篇 |
2000年 | 22篇 |
1999年 | 28篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有1401条查询结果,搜索用时 15 毫秒
941.
942.
采用密度泛函理论系统研究了二元等比锰硫团簇MnnSn(n=1-7)的结构和物理性质。首先得到了体系的最低能量结构以及相应的亚稳态同分异构体,讨论了团簇几何结构的生长模式和结构稳定性。通过电荷转移和差分密度分析发现Mn原子和S原子之间离子键和共价键的共存效应可以有效提高团簇结构稳定性。当原子数为奇数和偶数时,锰硫团簇的磁矩分别为5uB和淬灭状态,呈现出奇特的二元奇偶振荡现象,通过布局分析和态密度进一步探索了团簇磁性的来源和具体分布情况。 相似文献
943.
在空间光通信系统中,激光在大气中传输时容易受湍流效应影响,且接收端往往使用模场半径极小的单模光纤进行空间光耦合,导致光纤耦合效率降低,影响通信系统性能.为了提高接收端光纤耦合效率,结合随机并行梯度下降(SPGD)算法和少模光纤耦合解复用系统对动态湍流所引起的波前相位畸变进行补偿校正,并实现了传输距离为5 km的空间光通信数值仿真.仿真结果表明:在不同的湍流强度和风速条件下,未经SPGD算法校正时,两模光纤的耦合效率比单模光纤提高了0.5 dB~1.5 dB,相对标准差降低了0.03~0.4;经过SPGD算法校正后,两模光纤的耦合效率比单模光纤提高了0.4 dB~2.2 dB,中强湍流下,相对标准差降低了0.1~0.2.因此在空间光通信中,采用少模光纤进行耦合接收比单模光纤具有更好的耦合效果,有利于提高通信系统稳定性. 相似文献
944.
945.
A semi-analytical method for free vibration of straight orthotropic beams with rectangular cross-sections 总被引:1,自引:0,他引:1
On the basis of the two-dimensional elasticity equations with orthotropy, a semi-analytical method is proposed to analyze free vibration of straight beams with rectangular cross-sections. To this end, the state space method is combined with the differential quadrature method so that state equations with respect to state variables at discrete points are derived. The frequency equation for free vibration of straight orthotropic beams is then formulated. Numerical results are presented and compared with that available in the literature. The present method can be used to analyze either shallow or deep orthotropic beams with arbitrary end conditions. 相似文献
946.
947.
Kim-Hung Lam Sarah Sze-Wah Ho Pik-Ling Lam Johnny Cheuk-On Tang Zhao-Xiang Bian Albert Sun-Chi Chan Hua Li Wai-Yeung Wong Chung-Hin Chui 《中国化学快报》2014,25(8):1165-1168
This study reports the synthesis and characterization of quinoline derivatives. The synthesized quinoline compounds were applied to the dyeing treatment of acrylic fabrics. The color fastness to washing and light of quinoline compound-dyed fabrics was examined. Human skin HaCaT cell line was also used for the skin cytotoxicity evaluation of the quinoline compound-dyed acrylic fabrics. 相似文献
948.
A new spectrofluorimetric method is described for the determination of uric acid (UA), that can remarkably reduce the fluorescence intensity of the enoxacin (ENX)-terbium ion (Tb3+) complex at 545 nm. The reduced fluorescence intensity of Tb3+ ion at pH 5.7 is proportional to the concentration of UA. Optimum conditions for the determination of UA have been investigated. The linear range and detection limit for the determination of UA are 6.0 × 10?7–3.0 × 10?5 M and 1 × 10?7 M, respectively. The relative standard deviation (RSD) was 0.4% for 6 × 10?6 M UA (n = 11). The method is simple, practical and relatively free of interferences. It has been successfully applied to assess UA in serum at the level of 3 × 10?4 M with an RSD of 5–7% (n = 3). The results were evaluated by comparison with a common clinical spectrophotometric method using phosphotungstic acid as developer. 相似文献
949.
The Adsorption and Simulated Separation of Light Hydrocarbons in Isoreticular Metal–Organic Frameworks Based on Dendritic Ligands with Different Aliphatic Side Chains 下载免费PDF全文
Dr. Jiangtao Jia Lei Wang Fuxing Sun Xiaofei Jing Dr. Zheng Bian Prof. Lianxun Gao Prof. Rajamani Krishna Prof. Guangshan Zhu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(29):9073-9080
Three isoreticular metal–organic frameworks, JUC‐100, JUC‐103 and JUC‐106, were synthesized by connecting six‐node dendritic ligands to a [Zn4O(CO2)6] cluster. JUC‐103 and JUC‐106 have additional methyl and ethyl groups, respectively, in the pores with respect to JUC‐100. The uptake measurements of the three MOFs for CH4, C2H4, C2H6 and C3H8 were carried out. At 298 K, 1 atm, JUC‐103 has relatively high CH4 uptake, but JUC‐100 is the best at 273 K, 1 atm. JUC‐100 and JUC‐103 have similar C2H4 absorption ability. In addition, JUC‐100 has the best absorption capacity for C2H6 and C3H8. These results suggest that high surface area and appropriate pore size are important factors for gas uptake. Furthermore, ideal adsorbed solution theory (IAST) analyses show that all three MOFs have good C3H8/CH4 and C2H6/CH4 selectivities for an equimolar quaternary CH4/C2H4/C2H6/C3H8 gas mixture maintained at isothermal conditions at 298 K, and JUC‐106 has the best C2H6/CH4 selectivity. The breakthrough simulations indicate that all three MOFs have good capability for separating C2 hydrocarbons from C3 hydrocarbons. The pulse chromatographic simulations also indicate that all three MOFs are able to separate CH4/C2H4/C2H6/C3H8 mixture into three different fractions of C1, C2 and C3 hydrocarbons. 相似文献
950.
Solvent‐Free Syntheses of Hierarchically Porous Aluminophosphate‐Based Zeolites with AEL and AFI Structures 下载免费PDF全文
Yinying Jin Xian Chen Qi Sun Na Sheng Dr. Yan Liu Chaoqun Bian Fang Chen Dr. Xiangju Meng Prof. Feng‐Shou Xiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(52):17616-17623
Development of sustainable routes for synthesizing aluminophosphate‐based zeolites are very important because of their wide applications. As a typical sustainable route, solvent‐free synthesis of zeolites not only decreases polluted wastes but also increases product yields. Systematic solvent‐free syntheses of hierarchically porous aluminophosphate‐based zeolites with AEL and AFI structures is presented. XRD patterns and SEM images show that these samples have high crystallinity. N2 sorption isotherm tests show that these samples are hierarchically porous, and their surface areas are comparable with those of corresponding zeolites from hydrothermal route. Chosen as an example, catalytic oxidation of ethylbenzene with O2 shows that cobalt substituted APO‐11 from the solvent‐free route (S‐CoAPO‐11) is more active than conventional CoAPO‐11 from hydrothermal route owing to the sample hierarchical porosity. 相似文献